This invention relates in general to separation systems and, in particular, to an on-column junction for capillary columns and method for introducing substances into the capillary columns.
Capillary separation techniques such as capillary electrophoresis (CE) involving gel or liquid columns, and capillary liquid and gas chromatography have become important analytical techniques for the analysis of various complex sample mixtures. The sample mixtures analyzed are typically in tiny volumes, such as a few nanoliters. Hence, a key factor in such techniques is the development of suitable detection schemes for detecting very small amounts of the sample components. A number of detection methods have been in use. These include absorbance, fluorescence, chemiluminescence, electrochemical, radioactivity, and mass spectrometric detection. In each of these procedures, it may be advantageous to attach to the analytes a label or tag, or add components to the mobile phase, that aid in the separation/detection of the species of sample components.
Various connectors have been proposed for introducing substances into the capillary columns. Two such connectors introduce labels or tags post-column. See Rose, Jr. et al., J. Chromatoqr., Vol. 447, page 117 (1988); and Albin et al., Anal. Chem., Vol. 63, page 417 (1991). Post-column derivatization, however, results in peak broadening and dilution of the separated sample components and requires careful alignment of capillaries. All conventional connection schemes employ a connector to connect one or more side tubes to a main capillary, where the connector may be a separate or an integral part of the main tube and/or side tube. Another connector for introducing a substance is described in Pentoney et al., Anal. Chem., Vol. 60, page 2625 (1988), in which a T- or cross-shaped connector is proposed for introducing a substance into the capillary column prior to detection. Such a T-shaped or cross-shaped connector, however, requires that a tiny side capillary be connected to a hole drilled in the main separation capillary. Such alignment and connection process may be time-consuming and difficult to perform. It is therefore desirable to provide an alternative structure for introducing the substance such as a labeling reagent into the separation column.